Ferri-magnetic spinel bodies



y 1963 R. v. SARAKAUSKAS ETAL 3,096,288

FERRI-MAGNETIC SPINEL BODIES Filed Dec. 2:5, 1957 souo SOLUTION BINARY PHASE LINES v 0 O TEMP, RANGE- I050 C TO I250 C [NVENTORS RAYMOND V SARAKAUSKAS MASON C. COX NORMAN R. THIELKE A TTOR/VEV United States Patent 3,096,288 FERN-MAGNETIC SPINEL BGDIES Raymond V. Sarakausir'as, North ()lmsted, Mason C. Cox,

Bay Village, and Norman R. Thielke, North Olmsted,

Ohio, assignors to Union Carbide Corporation, a corporation of New York Filed Dec. 23, 1957, er. No. 704,732 11 Claims. (Cl. 252-625) This invention relates to a novel series of ferritic compounds possessing a variety of magnetic properties.

The present invention has for its main object the provision of novel ferritic compositions, certain properties of which may be maximized to render the same particularly useful in given applications.

Another object of the invention is to provide novel ferritic materials valuable for use as low loss cores in electric components operated at radio frequency.

The single FIGURE accompanying this disclosure is a triaxial composition diagram representing the oxide system Li O-TiO -Fe O and shows the compatible phase areas demarcating the field of this invention.

Ferrites are ceramic materials which respond to applied magnetic fields at frequencies as high as the megacycle range, and which possess an electrical resistance far superior to any magnetizable metal. Most ferrites yield X-ray diifraction patterns identifying them structurally with the mineral, spinel, MgOAl O The unit cell of this structure is a cubic arrangement of 32 anions (X), with 24 cations (A, B) distributed in certain interstices between the anions. In the so-called normal spinel unit cell, A type cations occupy lattice sides formed by four adjoining X anions, and, therefore, are said to be tetrahedrally coordinated; whereas B type cations occupy lattice sides formed by six adjoining X anions and are said to be octahedrally coordinated. The resulting formula for such an arrangement is AB X Also known are so-called inverse spinels, which correspond to the formula BABX In such compounds, half the B type cations occupy tetrahedral sites, while the remaining A and B type cations share octahedral sites.

The magnetic behavior of ferrites or spinels arises from the existence and relative alignment of unpaired spins of electrons in their orbits. Partial spin alignment in the direction of an applied magnetic field results in paramagnetic response in direct proportion to the magnitude In addition, cooperative, reinforcing spin of the field. alignments by many unpaired electrons closely adjoining one another result in ferromagnetic response to an applied magnetic field, as evidenced by the typical hystersis loop pattern. Similar cooperative reinforcing spin alignment for ions on the A site opposes the cooperative reinforcing spin alignment for ions on the B sites yielding a net A, B response to a field which may equalor exceed zero. This response is direct ferrimagnetism, and is, therefore, a function of the identity, distribution and :spacial relationship of ions in the crystallattice.

To elaborate on the occurrence of the unpaired electrons previously discussed, it is helpful to consider the periodic classificaiton of elements. The fourth period thereof includes a transition series which comprises those elements having electrons in the 3d orbit of the M shell. Unpaired electrons occur periodically as a result of the incremental addition of 3d electrons in the-series scandium through copper. Thus metallic potassium, calcium, scandium, titanium, chromium and manganese are increasingly paramagnetic in character; and iron, c0- balt and nickel are decreasingly ferromagnetic. When ionization occurs in the atoms of this transition series,

3,096,288 Patented July 2, 1963 the number of unpaired electrons is altered, and the magnetization changes accordingly.

It has been observed that ions of transition elements give rise to ferri-magnetic behavior when properly distributed on the alternative lattice sites available in a spinel structure. By contrast, other ions having no unpaired 3d electrons have been found in compounds which possess the spinel structure, but which do not exhibit ferrimagnetism. In common with the transition metal ions, such ions still conform to certain requirements for ion size and radius ratio, so that the spinel structure may be stated to require that tetrahedrally and octahedrally coordinated ions possess dimensions as follows:

Radius Angstrom Units Radius Ratio 0.34-1.12 A:B=0.6l.0 0.62-1.10 A:X=0.4-0.8

Accordingly, a ferrite could be chemically described according to prior art by the formula RO-Fe O (or RFe O4), Where R was a doubly charged ion, or was fractionally composed of two or more ions, for example, 30 percent zinc, 70 percent nickel, with the result that the compound might be written Zn Ni Fe 'O Every ferrite of this type has inherent properties such as initial permeability, maximum permeability, residual mag netism, coercive force, and Jordan loss constant. Simple combinations of ferrites containing different divalent ions allowed the researchers of the prior art to adjust given 'magnetic properties of ferrites, but only at the expense of other properties.

Another diificulty with the prior art ferritic materials of the RO-Pe O type was the necessity of employing temperatures of 1400 C. to 1600 C. At such high temperatures special furnaces and atmosphere controls were required, thereby increasing the cost of the end product.

The present invention is based upon the realization that one of the oxides present in the conventional ferrite formula may be replaced by two or more oxides, the cations of which have similar ionic bonding radius and cation to anion radius characteristics, or whose statistical parameters conform to these requirements. Thus it has been found that certain spinels tolerate this combinational replacement of ions, and that in a compound of the type ROFe O both the doubly charged R ion and the triply charged Fe ion may be replaced by appropriate compositions of cations. In contrast to the prior art line of ferrite compositions, which may be expressed as RO-Fe O and analogs thereof, the present invention provides novel substitutional series represented by the formula:

aLi O bRO cR 'O 0 to 5; and the sum of a+b+c ranges from 3 to 7.

Obviously the permutations of multiple oxide substitutions are very numerous, even if all the arrangements of oxides having no magnetically active cations present are excluded. In order that the magnetic spinel structure remain, it is necessary that the amount of R O not be less than a certain value unless other spinel forming materials such as RO-Fe O are present. This minimum value is approximately 10 mol percent of the final compound, which in the above formula is equivalent to a lower limit for c of about 0.1 (a+b+c), or when a equals 1, of about 0.1 (1+b+c). The present invention makes The properties of the ferrites of the invention are a function of the constituents present therein, of their mode of combination and of the individual property contributions from each constituent. In general, the characteristics contributed by each constituent reactant are additive.

By increasing the density of these ferrites by varying the kind of reactant, the fabrication procedure or the conditions of heat treatment, the permeability of the ferrites increases and their resistivity falls.

Briefly stated, the ferrites of the invention are prepared by finely dividing oxides or carbonates containing the desired ions, mixing the same in the dry state, wet milling a slurry of the reactants, drying the slurry, pre-calcining the dried slurry to a temperature below the particular final sintering temperature for these reactants, to effect substantially complete transformation thereof to the ferrite form; cooling the calcined mass, repulverizing the resulting calcine; forming a compressed body therefrom, preferably with plasticizers and bonding agents; firing the formed body at a temperature range of 950 C. to 1350 C. and then cooling. To obtain a completely single phased product, an excess of about 0.1 percent of lithium compound should be used. Omitting this excess, however, in no Way changes the properties of the products.

Instead of starting with oxides or carbonates containing the ions desired in the final ferrite formulation, such oxides may be precipitated in hydrated form from separate or mixed solutions of the desired salts. In a further variant of the invention, use is made of formates and oxalates which thermally decompose into extremely fine reactive crystals capable of accelerating ferrite formation and crystal growth.

In the case of certain ferrites, particularly those containing manganese oxides or amounts of Fe O exceeding the stoichiometric value for the ferrite, atmosphere control may be resorted to for the stabilization of the oxidation rate of the cation. In practice, atmosphere control is employed only during the cooling cycle or alternatively during a second reheat cycle at a lower temperature.

The compositions of the invention include, in summary, the following systems:

(a) System Li OTiO -Fe ,O

(l) Ferrospinel-type compositions along join Li O 5Fe O 2Li O 5Ti0 (2) Two-phase bodies in the compositional areas defined by the compatibility triangles immediately adjacent to the spinel-type solid solution join,

5Fe203Li2O F6203: (a) triangle Li O-5Fe O Fe O Li O Tiog, (b) triangle Li O-5Fe O F203-F6203, and triangle Li O 2Ti0 Fe O (3) Multiphase bodies in the compositional areas defined by the compatibility triangles next most adjacent to the ferrospinel solid solution join:

(a) triangle Li G- 5Fe O Fezog, and ([7) triangle Li O-2TiO -Fe O -FCZO3FCZO3 The utility of these compositions is indicated by the diminishing values of powder permeability of powder specimens of those compositions observed for compositions farther from the spinel solid solution join.

(4) The compositional area of marginal utility may be extended to include the compatibility triangles:

(5) At even more elevated temperatures, the miscibility gaps disappear, and the polygonal areas indicated are of interest:

Further latitude becomes available when other ferrites are incorporated into compositions embraced within the system Li O-TiO Fe O A number of these variants are indicated:

(aa) System Li OTiO -Fe O with compositional ranges as described in (a) above, but containing, in addition, a proportion of ZnO-Fe O in solid solution as single phase ferro-spinel compositions.

(ab) Related compositions employing CdO-Fe O (ac) More distantly related compositions employing other ferrites of normal type or mixed types, such as MgFe O NiFe O MnFe O and others of these types.

(ad) Complex systems, comprising a substituted ferrite, e.g., Li O-TiO -3Fe O plus a conventional inverse ferrite:

(l) CuO-Fe O (2) MgO-Fe O MDO'FCgOs (4) NiO-Fe O (5) CoO-Fe O (ae) Systems of further complexity, comprising a substituted ferrite, e.g., Li O'2TiO -Fe O plus a conventional inverse ferrite, as above, plus a conventional normal ferrite, such as zinc ferrite.

(b) System Li OMnO --Fe O (c) Compositions in which aluminum or other trivalent ions replace part of the trivalent iron.

(d) Compositions based on the oxide formulations of the type R O -R o -Fe O (e) Compositions based on oxide formulations of the general formula R,o -R o -R o,, where R 0 comprises a ferromagnetically active oxide such as C M11203, V 0 rare-earth sesquioxides, etc.

(f) Compositions based on spinel-type formulations other than those derived from the RO- R 0 prototype. These include:

(1) Derivatives of the formulation R O-RO (2) Derivatives of the formulation 2RO-RO etc.

(g) Compositions of the spinel structure and formulation in which a portion or all of the oxygen ions are replaced by divalent sulfur, selenium or tellurium ions or monovaient fluorine or hydroxyl ions, in appropriate stoichiometric proportion. Derivatives of these types predicted from the known degrees of similarity in ion size, bond character and electronic structure among these elements, evidenced by their mutually neighbormg position in the periodic system and by their frequent appearance in closely related structures.

It should be noted that the solid solution series between Li O-Fe O and Li O-TiO is cubic, NaCl type. The central solid solution series between Li O-5Fe O and 2Li O-5TiO shows the spinel structure or a close derivative of'it. The third solid solution series originating at gms. Li' CO 5.00 g-ms. T 54.00 gms. ZnO and 18 7.00 Fe O -TiO is found to be orthorhombic. The series of gms. Fe O These oxides and carbonates were mixed primary interest comprises the cubic, ferrospinel type comas a slurry with alcohol for approximately one hour, with positions between Li O-5Fe O and 2Li O-5Ti0 Rea Hobart N-50 mixer. The well mixed powders were acted compositions along this join showed only a single placedin fire cl-ay crucibles and calcined at 1050" C. for

phase solid solution of the ferrite type, whereas those to two hours in an air atmosphere. The ferrite powder-which either side of this join contained, in addition, a proporconsisted only of a spinel phase was milled with 100 cc. tion of the phase identified at the respective apex of the of alcohol in a porcelain mill with Alundum balls for adjoining composition triangle. The relative amounts five hours. The slurry was discharged and then permitted of the phases present are determinable by the usual lever- 10 to dry in an oven at 55 C. The fine-ground ferrite (250 arm relationship applied in phase equilibrium problems. gms.) was mixed thoroughly with a 2 percent solution Preliminary observations of magnetic activity were obof methocel (30 cc. of above-mentioned solution to 50 tained by measurements of inductance on solenoidal coils gms. of ferrite powder). The slurry was permitted to dry with and without a core comprising powdered composiat 55 C. to a hard cake which then was pulverized to tions of these ferrospinels. These were extended to many pass mesh sieve. Five percent water was added to this other compositions along the ferrospinel join and in adpowder containing the hinder; the mixture was sealed in jacent areas. The degree of magnetic activity to be exa jar and permitted to stand overnight. The powder then pected in the sintered compacts may be inferred roughly, was pressed as toroids under a load of 5000 p.s.i. at least, from the trends in effective magnetic permeability Toroids were fired on setters lined with platinum and of the powder core. 20 fired to a peak temperature of 1200 to 1225 C. for periods The systems of the present invention are especially of time ranging from 4 to 16 hours. Heating rate to this suitable as low loss cores in a variety of electronic comtemperature was 200 C. per hour in an air atmosphere, ponents used at radio frequency. Generally the mateand cooling was atthe normal free kiln cooling rate. rials of the invention have initial permeability values of Tonoidal specimens of the above composition exhibited 24 to 52 on toroids, and 20 to 40 on rods at a test he 25 initial permeability values of 715 when fired at 1225 C. quency of about one megacycle per second with associated for four hours and of 8 15 when fired at 1200 C. for ten resistivities of 10 to 10 ohm-centimeters. hours.

The magnetic and electric properties of typical novel What is claimed is: ferrite compositions are summarized in Table I. 1. A substituted ferrite material of spinel structure TABLE I Properties of Novel Ferrite Compositions Rods or Bars (Test Frequency-0.9 mc./s.) Toroids (Test Frequency1.2 mcJs.)

Code Number Sintering Percentage Efiective Quality Log Re- Sintering Percentage Effective Quality 'Iempera- Theoretical Relative Ratio sistivity Tempera- Theoretical Absolute Ratio ture 0. Density Initial Per- QulQo Ohm-cm. ture 0. Density Initial Per- Q lQ meability meability 1 Solenoidal coil and Q-meter; permeability of core calculated on basis of 100% coil occupancy. 1 Ratio of Q values of circuit element with and without core respectively. 3 National Electronics Permeameter and Q-meter. 4 Resistivity at 60 c./s. The compositions corresponding to the code numbers suitable for use as low loss cores in electric components, used are: said material having the formula:

M01 permit Code wherein b ranges from 0 to 5 and c ranges from about L10 TIO F 0 Num 0.1 (1+b+c) to 5; R stands for a cation selected from 2 1 2 a the group consisting of titanium and manganese, the sum of (1+b+c) being from 3 to 7. 13; 2 3:88 $3122 2. The substituted ferrite defined in claim 1 wherein 1 2( 3. 3% R represents titanium. 19:33 16:00 64:67 5417 3. A ferrite material comprising a composition which 20.00 20.00 50.00 5515 when represented on a molar three-phase diagram of Li O, Fe O and TiO as shown in the drawing, and when crystallized at a temperature in the range of 1050" 65 C. to 1250 C. lies on a straight line connecting the points Code Number Molar 00mm Li O-5Fe O and 2Li O-5TiO and which contains at least about 10 mole percent Fe O ifigjggifg 4. ferritic composition consisting essentially of a LnoioTioz-aFezo material having the composition L1 O-0.5T1O -4Fe O 242x, 7 A fer-ritic composition consisting essentially of a mater1al havmg the compos1t1on L1 O-TiO -3Fe O 6. A ferritic composition consisting essentially of a For a clearer understanding of the invention, the folmaterial having the composition Li O-TiO -2Fe O lowing example is given. A ferrite having the formula- 7. A ferritic composition consisting essentially of a lion-Lie 23Tlo 0 Zno. 0Fe2 1104, was prepared from 9.25 material having the composition Li O-2'liO -Fe O 7 8. A ferritic composition consisting essentially of a material having composition 17.34Li O-4.00TiO -78.66Fe O I 9. A ferritic composition consisting essentially of a material having the composition 18.00Li O 8.00Ti 74.00Fe O 10. A ferritic composition consisting essentially of a material having the composition 18.67Li O- 12.001 10 64.33Fe O 11. A fer-ritic composition consisting essentially of a material having the composition 19.33Li O-16:00TiO -64.67Fe O References Cited in the file of this patent UNITED STATES PATENTS 2,549,089 Hegyi Apr. 17, 1951 2,584,324 Bousky Feb. 5, 1952 20 2,640,813 Berge June 2, 1953 2,736,708 Crowley Feb. 28, 195

8 2,770,523 Toole Nov. 13, 1956 2,851,419 Gorter et a1 Sept. 9, 1958 FOREIGN PATENTS 713,370 Great Britain Aug. 11, 1954 735,375 Great Britain Aug. 17, 1955 752,659 Great Britain July 11, 1956 76,660 Netherlands Nov. 16, 1954 1,100,865 France Apr. 13, 1955 1,707,654 France Aug. 10, 1955 514,251 Canada June 28, 1955 OTHER REFERENCES 1. Institute of Electrical Engineers, Japan, November 1937, 1315.4, 5, 7.

Kordes et al.: Chem. Abs, vol. 46, column 4411, May 25, 1952.

Gorter: Proceedings of the IRE, December 1955, p. 1933.

Gorter: Philips Research Reports, vol. 9, No. .6, pp.

Weisz: Ceramic Ind., vol. 58, pp. -134, April 1952. 

1. A SUBSTITUTED FERRITE MATERIAL OF SPINEL STRUCTURE SUITABLE FOR USE AS LOW CORES IN ELECTRIC COMPONENTS, SAID MATERIAL HAVING THE FORMULA: 